Such a device includes the following features: a circular adapter, at least one connector extending downwards out of the adapter, to which connector a filter cartridge is attachable, a feed hole in the adapter, an outflow volume means above the adapter and communicating with the connector, a circular head above the adapter, a feed connector which extends upwards out of the head and communicates with the feed hole, and an outflow connector which extends upwards out of the head and communicates with the outflow volume means.
Such a device has become known in the prior art from U.S. Pat. No. 4,711,717, which issued Dec. 18, 1987 to this inventor. According to FIG. 6 thereof an adapter 62 is provided which comprises downwardly extending connectors 61. Filter cartridges 52 are attachable to these. The adapter has a feed hole 79. In the central zone 76 an outflow volume is provided. The head 78 with the feed connector 81 and the outflow connector 77 are also seen.
In this design the following was disadvantageous:
(a) When the filter was exhausted and the clamping plate 84 and the head 78 were removed, filtrate was able to spread out on the upper side of the adapter 62. However, in the case of some (dangerous) substances the washing already caused difficulties.
(b) The adapter too must be washed before further use.
(c) An extraordinarily high pressure must be applied if it is intended to obtain tightness, which also means tightness to gases, between the marginal zone of the adapter and the marginal zone of the head. If the adapter and the head are of synthetic plastic material, and if the pressure utilized to obtain tight conditions is very great, as is known the material can flow and the whole becomes unsealed in the marginal zones.
(d) If in the prior art it is intended to have surface sealing without the use of additional seals, then the surfaces facing one another must be extremely planar. The diameter of such devices is however of the order of size for example of 10-30 cm. and it is very difficult to produce planar surfaces cheaply by injection-molding or in any other way, which are plane in the sense of gas-tightness and/or fluid-tightness.
(e) Both the adapter and the head must be of extra-ordinarily rigid material and the zone between the outflow volume for the one part and the feed hole and the feed connector for the other part must also be sealed, even though here no sealing pressure can be applied between the clamping plate and the bowl. These conditions are extraordinarily difficult to fulfill. A slight excess pressure in the outflow volume can generate extraordinarily high forces, because it acts upon relatively large areas. If, therefore, for example, the adapter bends somewhat downwards, a gap occurs so that a short-circuit can occur between the feed connector and the outflow connector. Then this gap can no longer reduce to zero if there were particles in the fluid.
Excess pressures can also occur in the outflow volume, as for example when a non-return valve closes quickly or the like.
Then without doubt the pressure between the clamping ring and the clamping plate in the circumferential zone suffices to produce tightness, as before. It is not possible to determine whether a short-circuit has taken place in the interior or not, however.